DETROIT -- Authorities investigating a false bomb threat at a tunnel connecting Detroit and Canada said Friday that a surveillance video from a coffee shop near the phone booth where the call was made might offer clues about the caller.

The tunnel across the Detroit River was shut down for nearly four hours Thursday after a man calling from a street pay phone in Windsor, Ontario, warned of a bomb on the Canadian side, Windsor police Sgt. Matthew D'Asti said.

"We believe there's video from a coffee shop, Tim Hortons," he said. "I don't know the angle. We don't know if it's going to cover the phone booth in question."

Police inspected the phone for evidence and appealed to the public for help since the phone is near a park. The call was made around 12:30 p.m. EDT.

"All he really indicated is there was a bomb in the tunnel," D'Asti said.

The 82-year-old Detroit-Windsor Tunnel stretches about a mile across the river. About 4.5 million cars crossed in 2011.